The very nature of the liquid/paste product that you're applying is that it exhibits good adhesion to the designated substrate(s) and all types of timber are included in that, so the fact is, that whatever you gun out will indeed 'stick' to the 3C Wooden Wave Tooling Sticks. The old skool method of using saliva on the actual stick so as to create a barrier still holds true today but a better, more hygienic solution is to use washing up liquid or even better, a purpose-made tooling liquid such as these:  OTTO Smoothing Agent  / iLLBRUCK Tooling Agent. 

Technically yes you can! Obviously the 3C Wooden Wave Tooling Sticks are pre-cut to the various widths for ready-to-use ease and the widest of the 4 being 15mm is suffice for many standard joints but of course, at times the joint widths defy this standard so of course you can carefully double pass on the material making sure you don't get a line at the point where the stick stops wether it be in the middle or similar. Large joints commonly come in at 25mm or 30mm but if you're tooling off a monster 40mm plus mastic sealant joint either horizontal, vertical or even on a floor joint, a larger bespoke stick might be better.